Radio-frequency laser double-resonance spectroscopy of trapped171Yb ions and determination of line shifts of the ground-state hyperfine resonance

The paper reports on radio-frequency laser double-resonance experiments on¹⁷¹Yb ions confined in a cylindrically symmetric electrodynamic trap in the presence of helium buffer gas. The optical-excitation scheme relies on the selective excitation of a cycling hyperfine component of the = 370 nm resonance transition. Additional excitation of a transition at = 935 nm prevents population trapping of ions in the metastable² F _7/2 level. Using a maser reference, the ground-state hyperfine resonance frequency is measured under conditions of a systematic variation of confinement conditions. Kinetic temperatures and the resulting relativistic resonance shifts are inferred from the inhomogeneous broadening of the optical resonance transition. Shifts of the hyperfine resonance frequency due to quadratic Stark effect and collisions are determined. By extrapolation, the unperturbed transition frequency is determined as 12 642 812 118.471 (9) Hz.     

A new method to measure the wavelength of single-mode pulsed lasers with a scanning Michelson interferometer

We report on the possibility to measure the wave-lengths of pulsed single-mode lasers by means of a two-beam Michelson interferometer in motion [1,2]. The corner reflector moves with a nearly constant speed creating a path differenceL so thatL/C 1/, being the spectral width of the laser to be measured. The reference laser is a stabilized He-Ne (Spectra-Physics, model 117 A) to a precision of the order of two parts in 10⁹. The fringe pattern of the two beams (reference beam and measured beam) is sampled simultaneously with a repetition rate of 40 ms. With this new method, the frequency doubled injection-seeded Nd: YAG laser wavelength has been measured with an accuracy of the order of 1.5 in 10⁸3 × 10^–4 cm^–1 at 532nm.     

On the decrease in charge radii of multi-quasi particle isomers

We report changes in mean-square charge radii, δ〈r²〉$\delta 〈r^2〉$, magnetic moments and quadrupole moments for three multi-quasi particle isomers; ^97m2Y, ^176mYb and ^178m1Hf. All the isomers are observed to display a decrease in 〈r²〉$〈r^2〉$ compared to the lower-lying nuclear state on which the isomer is built. The decreases in 〈r²〉$〈r^2〉$ occur despite the isomers showing increases in quadrupole moment. Possible mechanisms for the effect, which is now seen for six multi-quasi particle isomers, are discussed.     

Dynamical properties of three component Fibonacci quasicrystal

We present a real space renormalization group (RSRG) method to study the lattice dynamics of a three component Fibonacci (3CF) quasicrystal. Phonon dispersion relations corresponding to different models of this lattice are obtained. Some features of the phonon dispersion curves are compared with experiments on real quasicrystal. It is observed that the positions of the strongest Bragg peaks calculated analytically are in perfect agreement with our RSRG calculations. Received 23 October 2000 and Received in final form 11 January 2001     

Dimensional crossover of quantum interference effects in thin quasicrystalline Al-Cu-Fe films

We present a study of the electrical transport properties of thin i-Al-Cu-Fe films. We observe clear signatures of a dimensional crossover in the temperature and magnetic field dependence of the conductivity for films thinner that ≃ 10³?. In particular for the thinnest sample the magnetoconductivity is strongly anisotropic, as is expected for the weak localisation contribution in two dimensions. These experiments show direct qualitative manifestations of the disorder induced quantum interference effects occurring in quasicrystals. Estimates of the electronic microscopic parameters are in accordance with those obtained in bulk samples. Their values and significance are discussed. Received 16 February 2001 and Received in final form 20 June 2001     

Numerical analysis of the dissipative two-state system with the density-matrix Hilbert-space-reduction algorithm

To investigate the influence of electronic interaction on the metal-insulator transition (MIT), we consider the Aubry-André (or Harper) model which describes a quasiperiodic one-dimensional quantum system of non-interacting electrons and exhibits an MIT. For a two-particle system, we study the effect of a Hubbard interaction on the transition by means of the transfer-matrix method and finite-size scaling. In agreement with previous studies we find that the interaction localizes some states in the otherwise metallic phase of the system. Nevertheless, the MIT remains unaffected by the interaction. For a long-range interaction, many more states become localized for sufficiently large interaction strength and the MIT appears to shift towards smaller quasiperiodic potential strength. Received 17 August 1998     

Shear banding instability in wormlike micellar solutions

Using NMR velocimetry and mechanical measurements we study the flow dynamics, within a cone-and-plate rheometer, of the wormlike micelle system, cetylpyridinium chloride/sodium salicylate (CPyCl/NaSal) at 100 mM/60 mM concentration in distilled water. Depending on precise conditions within the system, two classes of behaviour are observed, one in which the boundary between different shear rate phases fluctuates rapidly (on the order of tens of milliseconds) and one in which it migrates slowly with a time constant of many seconds. These modes of behaviour may depend on minor solution impurities, which presumably affect the detailed constitutive properties, but also on the externally applied shear rate within a given system. We argue that the slow migrations are governed by stress relaxation effects while the rapid migrations are flow driven and arise from interfacial instability. Received: 2 June 1998 / Received in final form and Accepted: 27 July 1998     

Specific mass shift of potassium 5P1/2 state

We have measured the isotope shift between ⁴¹K and ³⁹K in the 4s_1/2 → 5p_1/2 transition at 405 nm using saturation spectroscopy. Our measured isotope shift is 456.1 ± 0.8 MHz, implying a residual isotope shift (sum of specific mass shift and field shift) of −52.7 ± 0.8 MHz. We deduce a specific mass shift of −40 ± 5 MHz, which would imply that the 5p_1/2 state has a considerably larger specific mass shift than the 4p_1/2 state. We have in addition measured the 5p_1/2 hyperfine splitting for ⁴¹K.